A typical gas fired appliance, such as a boiler, includes a gas burner for generating heat. For example, with a boiler the burner is used for heating water. The appliance typically includes a draft hood or diverter. A vent from the draft hood exhausts products of combustion from the appliance. The vent may include a vent damper.
A typical gas fired appliance, in one known form, includes a relay control for operatively controlling the vent damper and the gas burner to open the damper if the gas burner is on. For example, when heat is called for the relay control sends a control signal to the vent damper to open the damper. Once the damper is open, then a signal is returned to the gas fired appliance to ignite the gas burner. Once sensed temperature exceeds the setpoint, then the control signal to the damper is terminated, causing the damper to close and removing the signal via the vent damper to the gas valve or burner control, causing it to shut off the gas supply to the burner. Closing the damper retains latent heat.
With current construction techniques, it is common for homes to be sealed tighter to provide fewer air flow paths between the homes' interior and exterior. This can result in depressurization of the home, or other building. Particularly, if other exhausting appliances such as a clothes dryer or exhaust fans are being used, then air is being drawn out of the house so that the home may become depressurized as there is no makeup air. When a building is depressurized, it will try to equalize by drawing in air from any openings to the outside including the gas fired appliance's venting system. This can result in the appliance's products of combustion spilling into the home. Some appliances, such as boilers, are equipped with a thermal switch to shut the boiler off if it is not drafting properly due to a blocked vent. However, this switch may not shut the boiler off if it is not drafting properly due to back drafting caused by cold air entering the home through the vent.
The present invention is directed to solving one or more of the problems discussed above, in a novel and simple manner.